There is presently an explosion in the demand for mobile communication devices, such as cellular telephones, two-way pagers, and wireless data transmission. Correspondingly, there is an ever increasing demand that such devices become smaller, lighter, and cheaper. Thus, there is always a desire when designing such communication devices to strive for designs that meet these criteria.
In many radio communication devices, upconversion is used to provide the modulated RF (radio frequency) output signal. For upconversion, an IF (intermediate frequency) source (typically in the 40 MHz to 300 MHz range) is mixed with an RF source. The IF source must be capable of being frequency modulated with deviations as high as 14 kHz. Typical IF sources have the following problems: (1) VCXOs (voltage controlled crystal oscillators) used in IF sources are difficult to modulate at these frequencies, and (2) conventional varactor-tuned oscillators are generally larger than desired and are not readily available.
Thus, there is a need in the art for an IF source that is small, inexpensive, capable of being frequency modulated, and easy to implement.